Mercury relay switching system



Dec. 15, 1959 1 J. MoN'roNl-I 2,917,641

MERCURY RELAY swrrcamc sys'rm Filed. nec.- 1e, 1957 taaie! United States Patent O MERCURY RELAY SWITCHING SYSTEM Liber J. Montone, Reading, Pa., assignor to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Application December 18, 1957, Serial No. 705,669

6 Claims. (Cl. 307-132) This invention relates to switching systems and particularly to such systems employing relays having mercury wetted contracts.

In some switching applications where it is desired to utilize relays having a fast armature transfer time, no contact bounce, high current capacity, and complete isolation between circuits connected to the relay contacts, conventional mercury relays which are otherwise well suited for the purpose are precluded for use because of the momentary bridging of the contacts by the mercury thereon during the transfer' of the relay armature from one contact to the other.

The object of this invention is a repetitively operated switching system utilizing a conventional mercury relay wherein the switched circuits may be electrically isolated from one another during the switching operation.

According to the general features of the invention, momentary short circuiting of two circuits connected to contacts of a mercury relay is avoided by connecting the contacts of a second relay in one of the circuits to be switched and controlling the relative percent break of the two relays so that the contacts of the second relay will always be open when the contacts of the mercury relay are bridged. Speciiically, the circuits to be switched are connected to the mercury wetted contacts of the mercury relay; the contacts of a second relay, operable between an open and a closed condition, are connected in series with one of the circuits and the corresponding contact of the rst relay. Asymmetric alternating or pulsating operating voltages are applied to the relays to open the contacts of the second relay slightly before the armature of the first relay is transferred from the corresponding contact to switch the circuits and, for the return operation, to transfer the armature of the trst relay back before the armature of the second relay recloses the serially connected circuit.

These and other features of the invention will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a schematic diagram of a system embodying the invention utilizing alternating current type mercury relays for controlling the switching operation;

Figs. 2 and 3 are graphs showing the variations in relay coil voltages with time for the system ofFig. l;

Fig. 4 is a schematic diagram of a relay coil energizing system utilizing D.C. type mercury relays for controlling the switching operation of the circuits of the system of Fig. l, and

Figs. 5 and 6 are graphs showing the variations in relay coil voltages with time for the system of Pig. 4.

For illustration purposes only, the invention, as disclosed in Fig. 1, is incorporated in a simpliied version of a test circuit for measuring the thermal resistance of a transistor 10. In this circuit, pulses of electrical energy are applied to the emitter 11 from the source 12, the collector 14 is grounded, and the base 15 is alternately connected, through the contacts of a conventional A.C. type ice mercury relay 16, to a twelve-volt supply 13 of a biasing circuit 18, and a microammeter 19 of a metering circuit 17. Bridging between the contacts of the metering and biasing circuits 17 and 18 cannot be tolerated, since the momentary application of the high voltage of the power supply 13 would injure the microammeter 19. The contacts (an armature and the contact b) of a second relay 20, which may be of the same type or have similar operating characteristics as relay 16, are connected in the power supply circuit 18 in series with the contact b" of relay 16 and are opened in order to eliminate the bridging effect by isolating the circuits 17 and 18 whenever relay 16 is actuated. The isolation between the circuits is accomplished by applying asymmetric energizing voltages V1 and V2 to the coils of relays 16 and 20, respectively, so that the percent make or dwell periods for the corresponding switched positions of the relays will be diierent whereby the contacts of the relay 20 will always be open (its armature held in a position) when the contacts of relay 16 are bridged.

The desired asymmetric voltages V1 and V2 are obtained from a voltage divider 23 connected across a source of alternating current 22 operating at a frequency corresponding to the desired switching frequency. One side of each of the relay coils is connected to the midpoint of the divider 23 while the other ends of the coils are connected to opposite ends of the divider. The coil of relay 16 is shunted with a diode 24 or other asymmetric conductive device and a variable resistance 25 while the coil of relay 20 is shunted with a variable resistance 26. Due to the variation in the impedance across the upper half of the voltage divider resulting from the non-linear impedance characteristics of diode 24, asymmetric voltages V1 and V2, as seen in Figs. 2 and 3 will be produced across the coils of the two relays. For a typical circuit, where the relays 16 and 18 are A.C. mercury relays of the Western Electric Company type 276E, the armatures will transfer at about plus or minus 18 volts (ie. -l-v or -v as seen in Figs. 2 and 3). As seen in Figs. 2 and 3, the circuit isolation is produced as a result of unequal contact dwell periods provided by the asymmetrical voltages. Thus, assuming at the outset 70 that the armatures of both relays are in the b positions, the transistor base 15 is connected through closed contacts b of the relays to the biasing circuit 18. Due to the steeper slope of V2 for the positive half cycle, the voltage V2 reaches +18 volts (+v) the relay operate value at time th before that of V1 at time which occurs at t2 Consequently, the armature of relay 20 transfers to contact a before time t2 when the armature of relay 20 is transferred to its contact "a and the momentary bridging occurs. Thus, during the interval between 71 and '72, the circuit 18 to the voltage supply 13 therein is open by the earlier transfer of the armature of relay 20 to 21, thereby preventing deleterious effects due to the momentary bridging of the contacts of relay 16. Likewise, when the aramatures again transfer, this time from a to "b, the voltage V1, due to its steeper slope in the negative half cycle, will reach the transfer value of 18, volts (-v) at t3 prior to t1 when voltage V2 reaches this value. The armature of relay 16 then is transferred back to contact b, and the bridging of these contacts is terminated before the armature of relay 2t) is moved from its open a position back to 11. The isolation intervals between t1 and t2, on the one hand, and t3 and "14 in the other, may be varied as desired by varying the relative values of V1 and V2 by changing the resistances 25 and 26 in shunt with the relay coils. In relays of this type the bridging intervals may be as long as one millisecond, consequently, the intervals t1-t2 and tf-L1 should be made slightly longer than one millisecond.

In the circuit shown in Fig. 4, a DC. type mercury relay 30, such as the Western Electric Company type 275B, is used in place of the AC. relay i6 of the system of Fig. 1, and a similar relay 3l. is used in place of relay 20, these relays operate at V volts and release at vr Volts. The asymmetric voltages V1 and V2 in this case are obtained by utilizing a common DC. pulse generator 33 which generates pulses at the desired switching trequency. The pulses are fed from the generator to first amplifier 3d for supplying operating pulses to relay 3i) and a second ampliier for supplying operating pulses to relay 3l. The amplifiers 3d and are of cod ventional design, for example, cathode follows individually modified by conventional means such that 'ie outp of 34 has a saw tooth shaped wave, wirle the output of amplier 35 has substantially a square wave shape. The pulses produced by the two amplifiers, while being synchronized from the common source 35, are asymmetrical and produce unequal contact dwell periods for the two relays as seen in Figs. and 6. Relay 3l. is actuated at t1 (when voltage V2 reaches o volts) prior to relay at t27 and relay is released at i3 (when voltage V1 reaches vr volts) prior to relay 3l at 14. Contact operation is identical as described in connection. with Fig. l. Thus, the intervals between il and t and between t3 and fr again provide the required isolation for the circuits l and (Eig. l). The length of the isolation intervals in this case may be varied simply by varying the magnitude of the output pulses of the amplifiers 3d and 35 by changing the values of suitable variable resistance elements 3d and in the outputs. For example, the dashed curve oi V1 shown in Fig. 5 (for a reduction in the resistance oi element Se), illustrates how the isolation interval between 12f and between taf-24, is made less than the intervals between fl-tz and tgl-rr for the higher value resistance of element 36.

vit is to be understood that the above described arrangements are simply illustrative of the application of the principles of the in eration. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and l within the spirit and scope thereof.

What is claimed is:

1. ln combination with a relay switching system having a rst relay with circuit-switching, mercury-wetted contacts which momentarily bridge whenever the relay is actuated, and a second relay having contacts operable between an open and a closed condition and connected in series with one of the circuits to be switched and the corresponding contact of the rst relay, oi means for periodically operating the relays comprising a source ol alternating potential, a passive network connected across the source for deriving two asymmetrically varying relay energizing voltages for controlling the relative perce break of the contacts of the relays to open said one of the circuits for a predetermined interval to isolate the switched circuit whenever the contacts of the first relay are bridged and to control the period during which the circuits are closed.

2. In a switching system for alternately switching one Circuit between a second and a third circuit and for providing an accurately controlled isolation interval between the switching operations, said system having a lirst relay with an armature movable between two mercury-wette contacts, means connecting said one circuit to the arms: ture, means connecting the second circuit to one of the contacts, means connecting the third circuit to the other contact, a second relay having mercury-wetted contacts operable between an open and a closed condition, and in 'is connecting the contacts of the second relay in series wit71 the second circuit and corresponding contact relay, of means for supplying operating volt relays to open the contacts of the second relay ure of the first relay is operated to switch c* circiut trom the second to the third circuit and fr the contacts of the second relay at a pretime before the armature of the first relay is back to re-establish the rst and second circuits, `ng a supply of alternating potential, a voltage divider energized by the supply, means for deriving asym ietrically varying relay operating potentials from the and means for applying the-derived ls to me relays. c a switching system for alternately switching one t between a second and a third circuit and for pr0- vio ig an accurately controlled isolation interval between g operations, said system having a first direct an armature movable between two mercureJ wetted contacts, means connecting said one cir- .iit to armature, means connecting the second circuit to one of the contacts, means connecting the third circuit to the other Contact, a second direct current relay having i'oercury-wetted contacts operable between an open and ition, and means connecting the contacts relay in series with the second circuit and ng contact of the rst relay, of means for i the second relay before the armature of the relay operated to switch the rst circuit from the --cond to ne third circuit and for reclosing the contacts ecoid relay at a predetermined time before the of the rst relay is transferred back to reroproducing periodic pulses, means for derivthe generated pulses, synchronized direct curlscs of direrent waveform for each of the relays. A system according to claim 3 having means for ig the relative magnitudes of the pulses to the relays for varying the duration of the interval between operation of the two relays.

fn according to claim 2 in which the relays onal alternating current mercury relays and the for operating the relays includes, a connection tween the hdd-point of the divider and one end of each o; erating coils of the relays, connections between the ends of the divider and the other ends of the relay operating coils and passive asymmetric impedance element in circuit with one of the coils.

6. A system according to claim 5 having at least one adjustable passive impedance element in circuit with one or the coils.

References Cited in the ille of this patent 

